Shock absorbers are used in conjunction with automobile suspension systems and other vehicle suspension systems to absorb unwanted vibrations which occur during operation of the vehicle. To absorb this unwanted vibration, shock absorbers are connected between the sprung mass (the body) and the unsprung mass (the suspension system) of the vehicle. A piston is located within a pressure tube of the shock absorber and is connected to the sprung mass (or possibly the unsprung mass) of the vehicle. The pressure tube is connected to the unsprung mass (or possibly the sprung mass) of the vehicle and is normally filled with hydraulic fluid. Because the piston has the capability to limit the flow of hydraulic fluid within the pressure tube when the shock absorber is compressed or extended, the shock absorber is able to produce a damping force which counteracts the vibrations which would otherwise be transmitted from the suspension (unsprung mass) to the body (sprung mass) of the vehicle.
A conventional dual tube shock absorber comprises a pressure tube with a piston disposed therein and a reserve tube surrounding the pressure tube. A piston rod is connected to the piston and it extends through the upper end of the pressure and reserve tubes. At the lower end of the pressure tube, a base valve is located between the pressure tube and the reserve tube. The base valve controls fluid flow between the working chamber defined by the pressure tube and the reserve chamber defined by the reserve tube. The damping force is created by the restricted flow of fluid through passages in the piston and valve plates which regulate passage of fluid between opposite sides of the piston within the working chamber.
Due to the piston rod being located on only one side of the piston, a different amount of fluid is displaced on the compression stroke as opposed to the rebound stroke. The difference in the amount of fluid is termed the rod volume. The rod volume of fluid is pushed out of the pressure tube, through the base valve and into the reserve tube during a compression stroke. During a rebound stroke, the rod volume of fluid flows in the opposite direction from the reserve tube, through the base valve and into the pressure tube.
The piston rod is supported at its lower end by the piston and is slidingly received at the upper end of the shock absorber by a rod guide. The rod guide thus functions as a slide bearing for the rod. The rod guide properly positions the piston rod within the pressure tube and also acts as a closure member for both the pressure tube and the reserve tube. In order for the smooth sliding of the piston rod through the rod guide, a slight clearance is formed between the inner periphery of the bearing portion of the rod guide and the outer periphery of the piston rod. This slight clearance allows for the hydraulic fluid to lubricate the interface between the piston rod and the rod guide.
In addition to locating the piston rod and closing the pressure and reserve tubes, the rod guide supports and locates a seal assembly which is designed to keep the hydraulic fluid within the shock absorber and also keep contaminants out of the shock absorber. The seal assembly normally interfaces between the reserve tube and the rod guide, between the rod guide and the piston rod and possibly between the reserve tube and the piston rod. The seal assembly is designed to keep hydraulic fluid within the shock absorber as well as keeping dirt and other contaminates from entering the shock absorber. The dirt and contaminants can be present and can adhere to the exposed portion of the piston rod.
There have been numerous seal systems designed and developed for meeting the difficult environmental and sealing requirements for shock absorbers. While these prior art seal systems have adequately performed in the field, the continued development of shock absorber seal systems has been directed towards providing similar or improved performance while reducing the manufacturing costs associated with the seal system.